The studies proposed herein will investigate the molecular basis of cell-cell adhesion in normal hepatocytes and changes which occur in this process during fetal development, liver regeneration and hepatocarcinogenesis. Monoclonal and polyclonal antibodies will be used as immunological probes to explore the structure, expression and function of cell-CAM 105, a 105kd cell adhesion molecule isolated from normal hepatocytes and glycoproteins associated with the desmoglea of rat liver desmosomes. Adhesive interactions will be measured by the rate of aggregation in suspension or the rate of formation of lateral contacts by cells attached to collagen gels. Antibodies reactive with components or epitopes functioning in cell adhesion will be recognized by their ability to block adhesive interactions. Immunochemical and biochemical techniques will be used in combination with a panel of monoclonal antibodies recognizing different epitopes to characterize structure and functional domains, nearest neighbors and steps in intracellular processing of cell-CAM 105 on normal and malignant hepatocytes. Similar techniques will be applied to the analysis of desmosomal glycoproteins. Immunocytochemical labeling methods at both the light and electron microscopic level will be employed to determine the in situ localization of cell-CAM and desmosomal components and changes occuring in the distribution of these components during adhesive interaction in vitro. The biological role of cell-CAM 105 and desmosomal glycoproteins will be assessed by examining adhesion related properties of expressor and nonexpressor tumor lines such as rate of aggregation, metastatic potential and microinvasion. DNA sequences encoding cell-CAM 105 will be isolated using the Lambdagt11 expression vector. These cloned DNA sequences will then be used in combination with blot hybridization methods, restriction analysis and DNA mediated gene transfer to examine the molecular events associated with the altered expression of cell-CAM 105 on transplantable hepatocellular carcinomas and following treatment with initiators and promotors of hepatocarcinogenesis. These studies should provide new information regarding the molecular basis for the altered interactions associated with the acquisition of the malignant phenotype.